First Lasing and Stable Operation of a Direct-Amplification Enabled Harmonic Generation Free-Electron Laser

Area of Science:

• Physics
• Laser Technology
• Spectroscopy

Background:

• High-repetition-rate seeded free-electron lasers (FELs) are crucial for advanced time-resolved spectroscopies.
• Conventional seeding methods require high-peak-power ultraviolet seed lasers (100 MW), limiting repetition rates.
• There is a demand for MHz-class FELs offering full longitudinal coherence and high photon flux in EUV and X-ray regimes.

Purpose of the Study:

• To demonstrate a novel direct-amplification enabled harmonic generation FEL.
• To achieve stable operation of an FEL driven by a low-peak-power seed laser (MW-level).
• To pave the way for MHz-class, fully coherent EUV and X-ray light sources.

Main Methods:

• Utilized a weak ultraviolet seed laser (0.75 μJ pulse energy).
• Employed a direct amplification technique within an 8-m-long modulator.
• Observed coherent harmonic generation and achieved saturation in the radiator.

Main Results:

• Demonstrated direct amplification of the seed laser pulse energy to over 10 μJ.
• Observed coherent harmonic generation up to the 12th harmonic of the seed laser.
• Achieved saturation of the 7th harmonic in the radiator.

Conclusions:

• Successfully demonstrated the first lasing and stable operation of a direct-amplification enabled harmonic generation FEL with a low-power seed.
• This method significantly reduces the seed laser power requirement, enabling higher repetition rates.
• Represents a critical advancement towards realizing MHz-class, fully coherent EUV and X-ray light sources for advanced scientific applications.